The invention relates to a spool valve comprising a valve housing with a connection port plate arranged therein or thereon and having a flat sealing surface facing into the interior of valve housing, a flat spool arranged on the sealing surface with which it makes sealing contact and which is able to be reciprocated parallel thereto between positions in which it respectively separates and joins together pressure fluid ducts opening into the sealing surface in the connection port plate, and drive means for said flat spool, such drive means having two operating surfaces facing in opposite directions of spool motion, such surfaces being on means connected with said flat spool and which are able to be acted upon by a driving fluid and are formed as part of the inner wall surface of an operating space with a variable volume, such wall being at least partly connected with the housing.
Such spool valves are finding an ever increasing field of application since they are characterized by a low wear rate and are appreciated because of their particularly sturdy design and long working life owing to the absence of so-called soft seals in the moving spool and it is in fact possible for the seal to be arranged as a surface seal on the connection plate. However there are some problems in connection with the operation of the valve, that is to say with the drive for causing the translatory displacement of the flat spool since so far the spool has been conventionally connected by way of a rod or the like extending in the direction of displacement with two secondary pistons, which are able to slide in bores in the housing and which each have an acting operating acted upon by the fluid under pressure. The O-rings or other sealing rings needed for the secondary pistons have turned out to have a high wear rate and frequently leakage occurs which interferes with the function of the valves. A further point is that the production of the spool drive is very involved and high in price and that furthermore the switching times possible with such a valve are relatively long owing to the mass of the secondary pistons.